Method of and device for the thermal working and processing of high-melting-point materials

ABSTRACT

A method and device for the thermal working and processing of high-melting-point materials, in which an electric arc is maintained in a gas stream between a primary electrode and an annular secondary electrode, and the arc plasma is constricted first by a flow aperture between the two electrodes and then by an outflow aperture of the secondary electrode, and the material is supplied to the arc plasma upstream of the flow aperture.

United States Patent [191 Essers et al.

METHOD OF AND DEVICE FOR THE THERMAL WORKING AND PROCESSING OF HIGH-MELTlNG-POINT MATERIALS Inventors: Wilhelmus Gerardus Essers;

Gerardus Jelmorini; Gerrit Willem Tichelaar, all of Emmasngel, Eindhoven, Netherlands U.S. Philips Corporation, New York, N.Y.

Filed: Sept. 14, 1972 Appl. No.; 288,921

Assignee:

Foreign Application Priority Data Sept. l7, i971 Netherlands 7112767 U.S. Cl 219/76, 219/121 P lnt. Cl. B23a 9/16 Field of Search 219/121 P, 76, 74, 75

References Cited UNITED STATES PATENTS 7/1963 Kugler et a] 2.19/12] P [451 AugQzo, 1974 Monduin-Monvalt 2 l 9/l 2l P 3,297,899 l/l967 Pratt et al 2l9/l2l P 3,569,661 3/l97l Ebeling et al. 219/121 P 3,575,568 4/l97l Tateno 2l9/l2l P 3,612,807 l0/l97l Liefkeus et al. 2l9/l2l P 3,632,952 l/l972 Rotalilo 2l9/l2l P Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm- Frank R. Trifari [57] ABSTRACT A method and device for the thermal working and processing of high-melting-point materials, in which an electric arc is maintained in a gas stream between a primary electrode and an annular secondary electrode, and the arc plasma is constricted first by a flow aperture between the two electrodes and then by an outflow aperture of the secondary electrode, and the material is supplied to the arc plasma upstream of the flow aperture.

6 Claims, 2 Drawing Figures ss-sl PAIENIEDwszomM snm 1er 2 METHOD OF AND DEVICE FOR THE THERMAL WORKING AND PROCESSING OF HIGH-MELTING-POINT MATERIALS BACKGROUND OF TI-IE INVENTION The invention relates to a method of and a device for thermally working and processing high-melting-point materials. An electric arc is maintained in a gas stream between a primary electrode and a complementary annular electrode, with the arc plasma constricted rst by a flow aperture between the two electrodes and then by an outflow aperture of the complementary electrode and in which the material is fed into the arc plasma and heated.

In this manner, plasma flames having temperatures of over 10,000K can be obtained at comparatively low gas speeds. As a result of these high temperatures, this method is particularly suitable for melting material having a high melting temperature and for working electrically non-conductive workpieces. According to such a method known from British Specification 845,41 l, a gas, a liquid or a powdered material can be introduced into the arc plasma laterally and downstream of the flow aperture but upstream of the outflow aperture. The drawback of this known method is that the material to be heated which is supplied in this manner is exposed to the energy of the arc plasma only over a small part of the arc length. ln addition, turbulences can occur in the arc plasma, in particular in the case of the supply of material in the form of a rod or wire.

SUMMARY OF THE INVENTION The object of the invention is to provide a method of the type mentioned in the preamble which does not have these drawbacks and in which the energy of the arc plasma is used in an optimum manner for heating the material. This object is achieved mainly in that the material is supplied to the arcplasma upstream of the flow aperture. As a result of this measure, the supplied material can be exposed to the energy of the arc plasma substantially throughout the length of the arc. Due to the improved heat transmission as compared with the known method, the supplied material can be heated at higher temperatures and/or be melted at a higher rate. The material to be heated can be supplied both in the form of a powder or grains and in the form of a rod or wire.

For carrying out the method according to the invention, a device is used which comprises a housing having a chamber which communicates with a gas inlet and in which the primary electrode is placed, a complementary annular electrode is provided with an outflow aperture and is located on the downstream end of the housing, and a diaphragm is placed between the two electrodes and provided with a flow aperture device furthermore comprises means for the connection of the electrodes to the terminals of a supply source and at least one supply duct for supplying the material to be heated. According to the invention this device is characterized in that the terminal part of the supply duct is situated upstream of the diaphragm. Due to the characterized location of the terminal part of the supply duct it is possible to bring the material to be supplied to in the immediate proximity of the primary electrode and to introduce it into the arc plasma on the part of the arc between the primary electrode and the diaphragm.

In a preferred embodiment of the invention, an optimum heat transmission to the material to be heated is obtained the supply duct is constituted by the axial bore of a tubular element which is arranged in the elongation of the common center line of the diaphragm and the complementary electrode. As a result of this it is possible to introduce the material axially into the arc plasma in the direction of the center of the flow aperture and of the outflow aperture. This embodiment is particularly but not exclusively suitable for the supply of materials in the form of a wire or rod, for the heating of which a better heat transmission is desirable than for materials in powder form.

A further preferred embodiment of the invention is characterized in that the primary electrode is in the form of a rod and arranged eccentrically relative to the diaphragm and the complementary electrode. This measure enables an optimum design of the primary electrode for simple assembly and dismantling, while the tubular element may be manufactured from a material best suitable for the supply of both electrically conductive and electrically non-conductive materials. The primary electrode may be arranged both parallel to and at an angle relative to the tubular element.

In another preferred embodiment of the invention the tubular element also constitutes the primary electrode. The combined function of the tubular element as a primary electrode and as a supply duct enable a very compact construction of the device.

In a further preferred embodiment of the invention which is particularly suitable for the supply of electrically conductive materials, the axial bore of the tubular element is provided with an electrically insulating linmg.

It is to be noted that it is known in plasma arc welding to introduce a supply wire axially into an arc plasma. In this case, however, the arc plasma is contracted only by the outflow aperture of a nozzle which moreover does not serve as a complementary electrode.

The invention will be described in greater detail with reference to the drawing. In the drawing:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the device for carrying out the method according to the invention;

FIG. 2 shows another embodiment of the device according to the invention.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings identical elements of the two embodiments are referred to by reference numerals that differ by the addition of the suffix a in FIG. 2. The device shown in FIG. l comprises a torch 1 composed of several components and having a cylindrical housing 3 with a chamber 5 the upper end of which is closed by a cap 7 of an electrically insulating material. A diaphragm 9 having a flow aperture ll is provided on the lower end of the housing 3. A rod-shaped nonconsumable primary electrode 13 is secured in the cap 7 and arranged eccentrically relative to the flow aperture 1l in the chamber 5. The inner wall of the chamber 5 is provided with an electrically insulating lining l5. A cylindrical nozzle 19 having a complementary annular electrode 2l which is provided with an outflow aperture 23 is secured to the housing 3 by means of an annular nut 17. The housing 3 and the nozzle 19 are electrically insulated relative to each other by means of an annular insulation element 25. A tubular element 27 which is secured in the cap 7 and of which the axial bore 29 constitutes a supply duct for material to be supplied, is arranged centrally in the chamber 5. The chamber 5, the diaphragm 9, the complementary electrode 21 and the tubular element 27 have a common centre line 31.

The housing 3 has a double-walled construction and comprises a cooling jacket 33 with connections 35, 37 for the inlet and outlet of cooling water. Similarly, the nozzle 19 is provided with a cooling jacket 39 with cooling water connections 41 and 43. The primary electrode 13 is preferably composed of two parts, namely the punctiform end 45 which is to be loaded by the electric arc and which constitutes the electrode proper and which is constructed from a high-meltingpoint metal, for example tungsten, and the part 47 which serves as an electrode holder and which is constructed from a thermally readily conductive metal, for example copper. The electrode holder 47 preferably comprises cooling ducts (not shown) and connections 49 and 51 for the inlet and outlet of water. The diaphragm 9 and the complementary electrode 2l are also constructed from copper. The diaphragm 9 is secured to the housing by means of a screw connection 53. The complementary electrode 21 is connected to the nozzle 19 in asimilar manner by means of a screw connection 55. As a result of this a simple mounting and dismantling of the diaphragm 9 and of the complementary electrode 21 is possible. The cap 7 furthermore comprises at least one inlet for first duct means tube 57 for the supply of a plasma gas. The nozzle 19 may moreover be provided with one or more connections 59 for the supply of a protective gas. Connection contacts 61 and 63 serve for the connection of the electrodes 13 and 21 to the terminals 65 and 67 of a supply source 69 via a high-frequency generator 71.

The embodiment of the torch according to the invention shown in FIG. 1 is particularly suitable for working rod-shaped or wire-shaped materials, both electrically conductive and electrically non-conductive materials. For that purpose the electrodes 13 and 2l are connected to the terminals 65 and 67 of the direct current supply source 69, the primary electrode 13 being usually connected to the negative terminal. However, the method according to the invention may also be carried out with the primary electrode connected to the positive terminal or to an alternating current supply source.

An arc is ignited by means of a high-frequency discharge between the two electrodes, which arc is maintained by the supply source 69. The arc can also be ignited by an auxiliary discharge between the primary electrode 13 and the diaphragm 9. A plasma gas is supplied through the inlet tube 57. As a plasma gas are used in practice inert gases, argon, helium, hydrogen and nitrogen, as well as mixtures thereof, while it is also possible to use oxidizing gases when special electrodes are used. The arc plasma 73 thus obtained is twice constricted, first by the flow aperture 1l of the diaphragm 9 and then by the outflow aperture 23 of the complementary electrode 21. A wire or rod 75 is fed axially into the arc plasma 73 through the axial bore^29 of theA tubular element or second duct means 27 in the direction of the flow aperture 11 and the outflow aperture 23. the material contacts the arc plasma 73 already upstream ofthe diaphragm 9 prior to entering the flow aperture 1l and traverses substantially the full length of the arc. Considering the rigidity of the rod or wire and the guiding effect of the tubular element 27, it is not necessary that the end 81 of the tubular element 27 is located in the immediate proximity of the primary electrode 13 and of the arc plasma 73. The material is melted in the arc plasma 73 and deposited in the form of droplets on a substratum. Feeding of the wire or rod may be carried out by means of driving rollers 77 which are driven by a motor 79 at a controllable speed, the rate of feeding being dependent on the desirable melting rate of the material. Through the connections 59 in the nozzle 19, a protective gas which may differ in composition from the plasma gas, can be supplied in the usual manner so as to obtain a sufficient protection of the melted material against oxidation. If desirable, the substratum may be further protected by an extra stream of protective gas. To be considered as protective gases, in addition to the rare gases, are other gases, for example, carbonic acid gas, gas mixtures of argon- /oxygen, argon/helium, argon/oxygen/carbonic acid, as well as hydrogen and nitrogen.

FIG. 2 shows another embodiment of the device according to the invention which differs from that shown in FIG. 1 only by a deviating shape of the primary electrode and which is particularlysuitable for the supply of material in the form of a powder or grains. The torch 85 of this embodiment also comprises a tubular element 87 which has an axial bore 89 constituting a feeding duct for the material and which also serves as a primary electrode. For that purpose the end portion 91 to be loaded by the electric arc and forming the electrode proper is made from a high-melting-point metal, for example tungsten. The remaining part 93 is made from a thermally readily conductive material, for example copper. The end 95 of the element is situated in the immediate proximity of the diaphragm 9a. Material 97 in powder form is fed, for example, by means of a carrier gas through the axial bore 89 centrally into the arc plasma 99. As soon as the material emerges from the bore 89 it is contacted with the arc plasma. The powder is melted in the arc plasma and deposited in the form of droplets on a substratum. lf the material to be fed is electrically conductive, the tubular element 87 is provided with an electrically insulating lining 101. This lining is of a material which can readily withstand temperature variations, for example quartz and alundum. Materials in the form of a rod or wire can also be melted by means of the torch according to this embodiment.

The invention will now be described with reference to a few examples: By means of the device shown in FIG. 1 in which the outflow aperture of the complementary electrode had a diameter of lO mm, aluminum oxide rods having a diameter of 1.5 mm were melted and deposited on a substratum at a current of 180A and an arc voltage of 28 V. The plasma gas was argon which was supplied with a quantity of 5 litres per minute. Dependent upon the rate of feeding, the rods melted at a rate of 2 to 8 grams per minute.

With the same type of torch, in which the outflow aperture of the complementary electrode had a diameter of 8 mm, zirconium oxide rods were melted at a current of A and an arc voltage of 30 V. The plasma gas used was argon which was supplied in a quantity of 4 litres per minute. The zirconium oxide 'rods melted at a rate of 10 grams per minute. With the same torch but at an arc voltage of 26 V and a current of 120 A, aluminium oxide rods having a diameter of 2.4 mrn were deposited at a rate of lO grams per minute.

The method and the device according to the invention are suitable for melting, depositing, spraying and welding, as well as for the evaporation and vapour deposition of materials having a very high melting point, both electrically conductive and electrically nonconductive materials, for example, for providing wearresistant, corrosion-resistant and heat-resistant layers on a workpiece. As already explained, the materials may be fed both in powder form and in the form of a wire or rod. In addition to the already mentioned materials aluminium oxide and zirconium oxide, tungsten, molybdenum, quartz glass, borate glass and other types of glass may be worked and processed. The annealing of materials in the form of a wire or rod is possible if the material is fed at a comparatively high speed.

What is claimed is:

l. Apparatus for plasma arc welding operable with a source of plasma gas, an electric power source, and a supply of material to be heated, and comprising: a housing defining therein a chamber having a top part and axially spaced therefrom an open downstream end, the chamber including tirst duct means for introducing said plasma gas from the source into said chamber, a primary electrode having a tip end within said chamber and axially spaced inward from said downstream end, a complementary annular electrode at said downstream end, this annular electrode including an outflow aperture therethrough, a diaphragm with a flow aperture therethrough positioned axially intermediate said two electrodes, means for connecting said electrodes to said electric power source, second duct means through which said material to be heated is moved into said chamber, this second duct means having a terminal part in said chamber up stream of said diaphragm.

2. Apparatus according to claim l, wherein said diaphragm aperture and said electrode aperture are generally coaxial and said primary electrode comprises a rod whose tip end is positioned eccentrically relative to said axis.

3. Apparatus according to claim 1, wherein said second duct means comprises a tube generally coaxial with said diaphragm aperture and the complementary electrode aperture axes.

4. Apparatus according to claim 3, wherein said second duct means tube also comprises said primary electrode.

5. Apparatus according to claim 4, wherein said second duct means tube defines a bore surface, the apparatus further comprises an electrically insulating lining onsaid surface.

6. A method of plasma arc welding for thermally working and processing high melting point material, comprising the steps of establishing in a chamber a stream of plasma gas flowing past a primary electrode and past and through the aperture of a complementary annular electrode axially spaced from said primary electrode, establishing and maintaing a plasma arc in said stream between said electrodes, constricting said arc with at least one aperture through which said stream flows between said electrodes, further constricting said arc by an aperture of said complementary electrode through which said stream flows, feeding said material into said arc upstream of said flow aperture between said electrodes. 

1. Apparatus for plasma arc welding operable with a source of plasma gas, an elEctric power source, and a supply of material to be heated, and comprising: a housing defining therein a chamber having a top part and axially spaced therefrom an open downstream end, the chamber including first duct means for introducing said plasma gas from the source into said chamber, a primary electrode having a tip end within said chamber and axially spaced inward from said downstream end, a complementary annular electrode at said downstream end, this annular electrode including an outflow aperture therethrough, a diaphragm with a flow aperture therethrough positioned axially intermediate said two electrodes, means for connecting said electrodes to said electric power source, second duct means through which said material to be heated is moved into said chamber, this second duct means having a terminal part in said chamber up stream of said diaphragm.
 2. Apparatus according to claim 1, wherein said diaphragm aperture and said electrode aperture are generally coaxial and said primary electrode comprises a rod whose tip end is positioned eccentrically relative to said axis.
 3. Apparatus according to claim 1, wherein said second duct means comprises a tube generally coaxial with said diaphragm aperture and the complementary electrode aperture axes.
 4. Apparatus according to claim 3, wherein said second duct means tube also comprises said primary electrode.
 5. Apparatus according to claim 4, wherein said second duct means tube defines a bore surface, the apparatus further comprises an electrically insulating lining on said surface.
 6. A method of plasma arc welding for thermally working and processing high melting point material, comprising the steps of establishing in a chamber a stream of plasma gas flowing past a primary electrode and past and through the aperture of a complementary annular electrode axially spaced from said primary electrode, establishing and maintaing a plasma arc in said stream between said electrodes, constricting said arc with at least one aperture through which said stream flows between said electrodes, further constricting said arc by an aperture of said complementary electrode through which said stream flows, feeding said material into said arc upstream of said flow aperture between said electrodes. 